This invention relates to laser systems and, more particularly, to frequency shifting of lasers.
Presently, there are many optical systems using 532 nanometer laser radiation which is typically obtained from a doubled Nd:YAG laser. The military, particularly, has many applications for such systems. Many of these applications require wavelength diversity in the visible portion of the electromagnetic spectrum. In particular, it is a requirement for particular military scenarios that the systems be capable of emitting two different wavelengths both of which are visible in order to impart to the systems greater resistance to countermeasures from an enemy. In such systems, it is of major import that the wavelengths can be varied such that an enemy does not become accustomed to particular wavelengths and, thus, provide equipment responsive to the particular wavelengths. To employ separate lasers at different wavelengths is impractical because of the accompanying increase in cost and complexity of such systems, particularly in systems where space is of a premium.
To alleviate the necessity of employing additional lasers, frequency diversity is currently being providing by down-shifting the 532 nm output of double Nd:YAG with laser dyes. In many cases, this has proved an unsatisfactory solution to the problem of frequency diversity since the use of dyes has many disadvantages. For example, they readily degrade by bleaching, thereby shortening the stability of such systems. The dyes must also be used in solvents which are flammable and toxic. The dyes additionally have poor thermal properties which leads to degradation of beam quality, and require plumbing to flow the liquids.
Accordingly, it is an object of this invention to provide improved laser frequency diversity.
It is another object of this invention to provide laser frequency diversity by using a solid state laser downconverter.